Method of granulating metals



Patented July 10, 1945 METHOD or GRANULATING METALS James P. A. McCoy,Milwaukee, Wis., assignor of one-half to Milwaukee Tool & Die Company,Milwaukee, Wis., a corporation of Wisconsin No Drawing. ApplicationFebruary 22, 1943,

- Serial No. 476,773

1 Claim. (CI. 8391) The present inventicn relates in general toimprovements in the art of metallurgy, and relates more specifically toan improved method of heat treating metals to granulate the same.

The principal object of my present invention is to provide an improvedprocess of readily and effectively reducing solid metals to granularcondition,

It frequently becomes desirable in the art of metallurgy, to. reducecertain solid metals and especially those having relatively low meltingpoints, to more or less powdered or granular condition. While somemetals may be granulated by impact or crushing, and others may bechemically reduced, while stil1 others may be granulated by heating themto molten state and then depositing the same in cool liquid or the like,none of these and other prior methods are entirely satisfactory eitherbecause of the excessive power consumption and other costs involved, orbecause the final product cannot be uniformly reduced without productionof excessive fines. Most of the previous metal granulating processesalso involve considerable waste of the materials due to undesirableoxidation of the metals, and can only be exploited with' the aid ofrelatively complicated and expensive equipment and materials. Some ofthe prior methods of granulating are also relatively slow and tedious byvirtue of the fact that they involve batch treatment, thus introducingobjectionable features into practically all of these previous processesof metal granulation.

It is therefore a more specific object of the present invention toprovide a simple, inexpensive and eillcient method of granulating solidmetals in an expeditious manner and with minimum waste of materials.

Another specific object oi my invention is to provide a new and usefulprocess of heat treating metals to uniformly pulverize or granulate thesame While avoiding excessive oxidation due to the heat treatment. I

A further specific object of the invention is to provide an improved andsimplified method of mechanically and continuously granulating certainmetals, without involving chemical action or treatment. v I

Still another specific object of this invention is to provide animproved process of rapidly converting solid metals or the like, touniform granular condition quickly, effectively and at minimum cost.These and other specific objects and advantages of my present invention,will be clearly apparent from the iollowing detailed description of theprocedure involved.

Although the invention may be restrictively described herein as beingadvantageously applicable in the treatment of certain metals with theaid of certain granulating agents, it is not my desire or intenttothereby unnecessarily limit the scope or utility of the improved methodwhich may also be applicable for and with the treatment of otherinvention is, however; commercially applicable materials notspecifically mentioned herein. The invention is, however, commerciallyapplicable primarily in the treatment of metals and alloys havingrelatively low melting points, that is, below 1000 C. p

In accordance with my present improved metal reducing or granulatingmethod, the metal to be reduced may be either in the form of bars,

ingots or a coating applied to other metal. This metal which is to bereduced is first heated so as to transform the same to a plasticcondition, while being constantly agitated in the presence of apulverulent wiping agent having mechanical afiinity for the plasticizedmetal. This wiping agent should be continuously brought in contact withand caused to rub against the metal as it becomes plasticized, andwillquickly convert the plastic metal-to more or less granular form andwill mechanically retain or hold the ranules; The mixture of granularmetal and wiping agent may then be removed from the heatingzone afterthe agent has become mechanically satu-- rated or laden with metallicparticles or granules, whereupon the granular metal may be readilyremoved from the agent and the latter may be reutilized for subsequentgranulation of other metal. is apt tobe undesirably affected byoxidation, the

wiping agent may be mixed with other granular or fibrous carbonaceoussubstance or material so as to provide a reducing atmosphere ofcarbondioxide and an abundant bulk mixture capable of maintaining themetal constantly covered and concealed from excess oxygen such as mightbe contained in the ambient atmosphere.

While various types of wiping agent may be used in carrying onmy'improved process; I have found that whengranulating metals such astin or solder having relatively low melting points,

pulverulent silica gel or flour, bentonite, carbon black, siliconcarbide, various clays, or other materials. reduced"to finely divided orpulverulent condition such as mesh or finer, may be utilized. I havealso discovered that-the useof difierent wiping agents result invariation in In cases where; the metal being treated,

the size of the metal granules, and the desired agitation and wipingaction may be readily obtained in an externally heated rotary drumthrough which the mixed metal and wiping agent can be continuouslyadvanced with a cascading action. The wiping agent may be circulatedthrough the heating drum several times before or solder is being reducedto granular condition,

this final separation can be quickly efiected by flotation in a bath ofwater wherein the tin or solder granules will settle by gravity whil thewiping mixture may be floated oil! and reclaimed for further use. Theforegoing procedure will permit rapid and continuous reduction of largequantities of metal to uniformly granulated condition with the aid ofvery simple equipment and at extremely moderate cost.

From the foregoing detailed description it should be apparent that mypresent invention provides an extremely simple and eificient method ofgranulating various metals without resorting to impact or crushing, andwithout excessive heating. Relatively inexpensive materials may beutilized in compounding the wiping mixture,

and the metal may be reduced to either coarse or line granular condition'by selecting the proper wiping agent, but in all cases the reduction isuniform and may be rapidly effected. Undeairable oxidation may also beeliminated by selecting proper canbonaceous materials for producing thedesired reducing atmosphere while incidentally increasing the volume ofthe wiping mixture, and since the process is purely mechanical, thewiping ingredients can be quickly removed from the granulated orpulverized metal and reclaimed for further use. In order to produce bestresults and rapid action, the primary wiping agent should be fiufly andloose and incapable of packing, so that it will intimately contact allportions of the plasticized metallic surfaces. Actual exploitation ofthe improved method has demonstrated that tin and solder and othermetals having relatively low melting points, can be quickly andeffectively granulated in but a few minutes, and that a uniformlygranular product results.

It should be understood that I do not desire to limit the presentinvention to the exact steps of the method or to the treatment of anyparticu lar material referred to and described herein for variousmodifications within the scope of the appended claims, may oocur topersons skilled in the art.

I claim:

' The 'method of producing granulated metal,

which comprises, agitating the solid metal having melting points below1000 C. while completely concealed in an abundance of saw dust andheating the mass to plasticize the metal. mixing silica gel with theconcealed and plasticized metal to granulate the latter, and finallyseparating the granulated metal from the mixture. JAMES P. A. MCCOY.

